Injection of antigen into the anterior chamber of the eye induces suppression of antigen-specific DTH, called anterior chamber-associated immune deviation (ACAID). It has been shown that the spleen is required for the induction of ACAID and detecting the ACAID-inducing signal from the eye. To examine the in vivo role of spleen cells, fractions of spleen cells were adoptively transferred into splenectomized mice. The present study showed that DTH was not suppressed in splenectomized mice, but was inhibited in splenectomized mice transferred with a primed CD4+ T cell-containing fraction of spleen cells. This indicates that the splenic CD4+ T cells comprise the regulatory T cells for the DTH response. When we examined the cytokine profile of the infiltrating T cells in the eye of primed mice by reverse transcriptase-polymerase chain reaction (RT-PCR), we found that they expressed IL-4, IL-10 mRNA (Th2 type), but not IL-2 and interferon-gamma (IFN-γ) mRNA (Th1 type). By contrast, T cells which can elicit normal DTH response expressed IL-2 and IFN-γ mRNA. These results suggest that splenic CD4+ T cells comprising the regulatory phenotype are required for the induction of ACAID, and that a DTH response to the antigen may be prevented by Th2-dominant CD4+ T cells.